EM 1110-2-1100 (Part V)
31 Jul 2003
Plots of the placed advanced fill and renourishment volume throughout the life of each of the projects
simulated are shown in Figure V-4-20. Volumes shown in this plot exclude the design fill volume of 960,000
cu m contained within the project limits and small 400-m transitions at the ends of the project. The volume
values include the volume contained in the transition zones that are constructed initially, and advance
nourishment placed within the project limits needed to see that the design width is not compromised during
the first renourishment cycle. As can be seen in Figure V-4-20a, in the absence of background erosion, the
required renourishment volume is expected to decrease slightly over the life of the project. With a
background erosion rate of 0.5 m/year the required renourishment volume is seen to remain nearly constant
throughout the project life. Most project sites experience background erosion.
Results indicate that the advance fill volumetric requirement is nearly twice the volumetric
requirement of subsequent renourishments, and nearly three times as much for the shortest
renourishment interval, or 3 years. The advance fill volume includes the volume initially placed in
the transition sections. The explanation for this result is that a substantial volume of material is
required to provide a natural transition from the adjacent shorelines to the more seaward-advanced
project shoreline. This volume of material is required at the time of initial construction, as part of
the advanced fill. Without the transition sections, high end losses at the project transitions would
have compromised the design berm width over a significant length of the lateral portions of the
project. Subsequent renourishments do not require this additional volume because the adjacent
beaches are already prograded toward the design beach width. Part V-4-1-h examines the subject of
fill transitions in more detail.
Figure V-4-21 provides plots of the cumulative volume placed for each of the beach nourishment
projects simulated. Results indicate that the cumulative beach nourishment volume requirement for
a 50-year project life is nearly the same regardless of the renourishment cycle (at least for the
renourishment intervals tested, which span the typical range of most beach-fill projects). A detailed
examination of the model output indicates that the average annual rate of loss of sand from the
project area increases only slightly as the renourishment cycle increases (3 or 4 percent difference
between annual loss rates for 3- and 9-year renourishment cycles). Selection of a renourishment
cycle for Federal projects is made through an optimization process that optimizes the amortized initial
construction costs and the annual cost of periodic renourishment to minimize the total average annual
equivalent cost. Selection of renourishment volumes/intervals is typically done based on average
expected losses over the life of the project. Selecting a longer renourishment interval, with strict
adherence to amortized life-cycle-cost based selection, may reduce flexibility in dealing with annual
variations in loss rates, which might be caused by several years of higher than normal storm activity,
or design deficiencies discovered within the first few years following construction. From both
engineering/design and monitoring/maintenance perspectives, 3- to 4-year renourishment cycles are
desirable. If longer renourishment intervals are desired from an economic perspective, it is prudent
to plan a short first renourishment interval (about half the optimized interval, or 3 to 4 years,
whichever is smaller).
If the volume remaining within the project area is subtracted from the cumulative placed volume, one
can estimate the cumulative spreading losses. In the simulations without background erosion, the
cumulative spreading losses range between 2.75 to 2.83 million cu m of sand, depending on the
renourishment cycle. However, the simulations that included the effect of a 0.5 m/year background
erosion rate indicate substantially higher cumulative losses, between 6.36 to 6.68 million cu m of
sand, depending on the renourishment cycle. Some past projects have underestimated renourishment
requirements by assuming that a historically based volumetric rate of erosion within the project
domain can be used to estimate the required renourishment. This assumption incorrectly neglects
the effect of background erosion outside the project on project end losses. For example, the
V-4-56
Beach Fill Design
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